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Two king post trusses linked to support a roof. Key:1: ridge beam, 2: purlins, 3: common rafters. This is an example of a "double roof" with principal rafters and common rafters. A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof.
Engineered lumber can be cut to length and installed much like sawn lumber; the flitch requires shop fabrication and/or field bolting. This, coupled with a much increased self-weight of the beam (11.4 pounds (5.2 kg) for engineered wood vs. 25.2 pounds (11.4 kg) for a flitch beam), decreases the viability of the system.
A hammer-beam is a form of timber roof truss, allowing a hammerbeam roof to span greater than the length of any individual piece of timber.In place of a normal tie beam spanning the entire width of the roof, short beams – the hammer beams – are supported by curved braces from the wall, and hammer posts or arch-braces are built on top to support the rafters and typically a collar beam.
A view of a roof using common purlin framing. The purlins are marked in red. This view is from the inside of the building, below the roof. The rafters are the beams of wood angled upward from the ground. They meet at the top of the gable at a ridge beam, which has extra bracing to attach it to the rafters.
Depending on the roof covering material, either horizontal laths, battens, or purlins are fixed to the rafters; or boards, plywood, or oriented strand board form the roof deck (also called the sheeting or sheathing) to support the roof covering. Heavier under purlins or purlin plates are used to support longer rafter spans.
A cruck or crook frame is a curved timber, one of a pair, which support the roof of a building, historically used in England and Wales. This type of timber framing consists of long, generally naturally curved, timber members that lean inwards and form the ridge of the roof. These posts are then generally secured by a horizontal beam which then ...
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Greek: the ridge height is 1 ⁄ 9 to 1 ⁄ 7 the span (an angle of 12.5° to 16°); Roman: the ridge height is 2 ⁄ 9 to 1 ⁄ 3 the span (an angle of 24° to 34°); Common: the rafter length is 3 ⁄ 4 the span (about 48°); Gothic: the rafters equal the span (60°); and; Elizabethan: the rafters are longer than the span (more than 60°). [7]